According to Wikipedia:
``Two parties dominate Malta's polarized and evenly divided politics: the Nationalist Party tit Nazzjonalista rence Gonzi, and the Malta Labour Party invariably generate a widespread voter turnout exceeding 96%. The margin between the two parties is so narrow that a 52% share of the votes can still be considered a "landslide" for the winning party.''
Evidently, IRV leads to 2-party domination, and in Malta's case a highly severe type, even though Malta contains many multimember districts with STV PR elections. [Later note: Malta as of 2006 apparently no longer uses IRV in the sense that every district is now a 5-member district.]
See more about Malta's voting systems and politics.